Nahlsgen (registered trademark) or GGsTop (generic name: DL-2-amino-4-[(RSp)-(3-carboxymethylphenoxy)(methoxy)phosphoryl]butanoic acid) is known as an excellent GGT inhibitor (for example, Patent Literature (PTL) 1).
Nahlsgen is a mixture of four optical isomers. However, there has not yet been known a method for completely separating the four optical isomers from the mixture. In addition, Nahlsgen at room temperature is not crystallized, but is in an oily state; and an amorphous powdery solid, which is finally obtained through lyophilization, is deliquescent and is liable to decompose at room temperature. The powdery solid therefore has to be stored in cold storage or frozen storage and is very hard to handle.